The method for measuring a chemical substance in a liquid sample include for example electric and optical measurement methods in which a substance having molecular selectivity is immobilized beforehand, a liquid sample is allowed to flow thereon, and a bound molecule is selectively detected.
Optical methods involve techniques using a probe molecule to which a fluorescent substance or a light-absorbing substance is immobilized beforehand. In addition, methods using a total reflection optical system are available by which binding of a molecule and an immobilized substance having molecular selectivity can be directly observed. These methods are known as methods in which an excited evanescent wave is used as a probe light, and binding in the vicinity of the surface is directly measured with high sensitivity. Most commonly used method among the total reflection-type optical systems is Surface Plasmon Resonance (SPR) measurement method, which utilizes a sample's absorption of a surface plasmon excited by total reflection of a metal thin film formed on a substrate surface, and total reflection-type attenuation measurement method, which utilizes a sample's absorption of an evanescent wave excited by total reflection due to a difference between a substrate surface and a sample in a refractive index.
To measure a liquid sample with a total reflection optical system, means of forming a passage on a substrate and immobilizing a probe molecule in the passage beforehand or forming a passage on an immobilized probe molecule is taken. Then, a liquid sample is passed through this passage. Based on an interaction between the immobilized probe molecule and a substance to be measured in a sample, whether the substance to be measured is contained in the sample can be determined, and the substance to be measured can be further quantified using the above-mentioned total reflection optical system (for example, the amount of a specific chemical substance contained in a liquid can be determined from the condition of a reflected light of a measurement light irradiated on the above-mentioned passage).
Furthermore, measurement using a total reflection optical system and a substance having molecular selectivity appears to be more suitable for short-time low-cost screening that is also suitably used in a field test than high-cost, high-precision, and high-sensitivity analyses represented by chromatography. A simple device for total reflection optical measurement has already been developed and described in, for example, Patent Document 1.
[Patent Document 1] Japanese Patent Laid-Open No. 2002-214131